The present invention relates to flat deck vibrating screens of the type particularly used for the fine screening of oil well drilling muds, and in particular to a tensioning arrangement for tensioning the relatively fine mesh screen cloth used in the vibrating screen.
It is well known in the rotary drilling of oil wells that it is extremely important to remove drilled solids, i.e., cuttings, cavings, sand, and shale, from the mud used during the drilling operation. Recirculation of the drilled solids can create viscosity and gel problems in the mud, as well as increased wear in the mud pump and mechanical equipment employed during the drilling operation. Solids control thus becomes one of the most important phases of mud control.
A shale shaker or vibrating screen has proven extremely successful in removing drilled solids from the mud. Generally, a fine screen cloth of 60 to 100 mesh is employed with the vibrating screen. The screen generally comprises at least two overlying layers of screen cloth.
The frame of the vibrating screen is resiliently suspended or mounted upon a support and is caused to vibrate by means of a vibrating mechanism, for instance a revolving unbalanced weight carried by a rapidly rotating shaft disposed transversely of the frame. Vibration of the frame caused by the vibrating mechanism results in the fine mesh screen cloth moving in an axial or longitudinal direction with respect to the frame.
Heretofore, the screen cloth has been tensioned in a direction transverse to the path of movement of the screen cloth produced by vibration of the frame. In vibrating screen devices having at least two overlying layers of relatively fine mesh screen cloth, it has been found that such screen cloth wears out at a relatively rapid rate requiring shut down of the device and replacement of the screen cloth. Obviously, due to the importance of the device during the drilling operation, any shut down thereof may prove quite detrimental to the drilling operation. Further, the relatively rapid wear of the screen cloth increases the cost of operating and maintaining the vibrating screen.